Marketable Securities - Summary of Marketable Securities Including Accrued Interest Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 151,521	$ 90,404
Gross Unrealized Gains	63	57
Gross Unrealized Losses	(242)	(70)
Fair Value	151,342	90,391
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,052	19,528
Gross Unrealized Gains	1	6
Gross Unrealized Losses	(39)	(13)
Fair Value	26,014	19,521
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	74,614	35,045
Gross Unrealized Gains	23	11
Gross Unrealized Losses	(174)	(47)
Fair Value	74,463	35,009
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	964	1,093
Gross Unrealized Gains	36	25
Gross Unrealized Losses	0	(1)
Fair Value	1,000	1,117
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,358	88
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(10)	0
Fair Value	7,348	88
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,888	25,199
Gross Unrealized Gains	1	15
Gross Unrealized Losses	(16)	(7)
Fair Value	15,873	25,207
Bank certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,645	9,451
Gross Unrealized Gains	2	0
Gross Unrealized Losses	(3)	(2)
Fair Value	$ 26,644	$ 9,449